This invention relates to electrotherapy circuits and in particular to a method for configuring an external defibrillator based on environmental characteristics.
Electro-chemical activity within a human heart normally causes the heart muscle fibers to contract and relax in a synchronized manner that results in the effective pumping of blood from the ventricles to the body""s vital organs. Sudden cardiac death is often caused by ventricular fibrillation (VF) in which abnormal electrical activity within the heart causes the individual muscle fibers to contract in an unsynchronized and chaotic way. The only effective treatment for VF is electrical defibrillation in which an electrical shock is applied to the heart to allow the heart""s electrochemical system to re-synchronize itself. Once organized electrical activity is restored, synchronized muscle contractions usually follow, leading to the restoration of cardiac rhythm.
FIG. 1 is an illustration of a defibrillator 10 being applied by a user 12 to resuscitate a patient 14 suffering from cardiac arrest. In cardiac arrest, otherwise known as sudden cardiac arrest, the patient is stricken with a life threatening interruption to their normal heart rhythm, typically in the form of ventricular fibrillation (VF) or ventricular tachycardia (VT) that is not accompanied by a palpable pulse (shockable VT). In VF, the normal rhythmic ventricular contractions are replaced by rapid, irregular twitching that results in ineffective and severely reduced pumping by the heart. If normal rhythm is not restored within a time frame commonly understood to be approximately 8 to 10 minutes, the patient 14 will die. Conversely, the quicker defibrillation can be applied after the onset of VF, the better the chances that the patient 14 will survive the event.
The defibrillator 10 may be in the form of an automatic external defibrillator (AED) capable of being operated by users with a wide variety of skill levels ranging from first responders to physicians, including emergency medical technicians trained in defibrillation (EMT-Ds), police officers, flight attendants, security personnel, occupational health nurses, and firefighters. AEDs can also be used in areas of the hospital where personnel trained in ACLS (advanced cardiac life support) are not readily available.
Having a simple, easily understood user interface in an AED is particularly important in applications where the first responder may have only infrequent need to use the AED. Because training and refresher courses may be relatively infrequent, coupled with a high stress emergency situation in which the AED is designed to be used in, the user interface design is therefore critical.
In more recent AED designs such as the Heartstream Forerunner(copyright) defibrillator, the AED functions have been logically grouped into step 1, xe2x80x9cpower onxe2x80x9d; step 2, xe2x80x9canalyzexe2x80x9d; and step 3, xe2x80x9cshock.xe2x80x9d More sophisticated audio prompts have been added in addition to the visual prompts provided by the LCD display. The transition from step 1 to step 2 may be initiated by the defibrillator, such as upon detection of patient contact between the defibrillation electrodes to begin the ECG analysis as soon as possible. Proceeding from step 2 to step 3 according to the AED personality requires the user to press a shock button upon recognition of a shockable rhythm by the ECG analysis algorithm. In this way, the AED personality is commonly understood to mean semi-automatic rather than fully automatic defibrillation.
The step 1, 2, and 3 methodology, with some variation among manufacturers, is commonly understood and accepted as the AED personality. After step 3, the AED can continue the ECG analysis as a background process to watch for shockable rhythms and alert the user 12.
In FIG. 1 according to step 1 of the AED personality, the defibrillator 10 is turned on and a pair of electrodes 16 is applied across the chest of the patient 14 by the user 12 in order to acquire an ECG signal from the patient""s heart. According to step 2 of the AED personality, the defibrillator 10 then analyzes the ECG signal to detect ventricular fibrillation (VF). If VF is detected, the defibrillator 10 signals the user 12 that a shock is advised. According to step 3 of the AED personality, the user 12 then presses a shock button on the defibrillator 10 to deliver the defibrillation pulse to resuscitate the patient 14.
The defibrillator 10 thus forms a nexus between a population of patients 14 and a population of users 12. The behavior of the defibrillator 10 is critical in maximizing both the efficacy of the resuscitation effort and patient safety across the two populations and also across the variety of circumstances in which the defibrillator 10 may be used. It has been found that the behavior of the defibrillator 10 may be optimized according to a set of meaningful parameters across the population of patients 14, the population of users 12, and the various circumstances in which the defibrillator 10 may be employed.
The configuration parameters of the defibrillator 10 that determine the behavior of the defibrillator 10 are often complex and arcane, bearing little resemblance to the environmental characteristics. It would be desirable to be able to map the set of environmental characteristics to the set of configuration parameters to ease the process of configuring the defibrillator 10.
The population of patients 14 spans the entire human population since sudden cardiac arrest (SCA) can potentially affect anyone. The human population can be further categorized using environmental characteristics that have been found to be meaningful for defibrillation and resuscitation purposes. For example, the patient 14 may have a transthoracic impedance (xe2x80x9cpatient impedancexe2x80x9d) that spans a range commonly understood to be 20 to 200 ohms. It is desirable that the defibrillator 10 provide an impedance-compensated defibrillation pulse that delivers a desired amount of energy to any patient across the range of patient. The patient""s age group, generally categorized as infant, adult, and geriatric, may determine the minimum amount of energy needed for effective defibrillation as well as the appropriate resuscitation protocols that determine how the defibrillator is to be applied. It would be desirable that the behavior of the defibrillator 10 be optimized according to a set of patient characteristics.
The population of users 12 includes first responders with little or infrequent training in the use of defibrillators, designated first responders who may have more frequent training as a secondary part of their jobs, and EMTs, paramedics, and physicians who have higher levels of medical training and more frequent opportunities to use defibrillators. This classification takes into account the level of user (operator) training and as well as the familiarity of the user 12 with the defibrillation process. It would be desirable that the behavior of the defibrillator 10 be optimized according to the type of user 12.
The circumstances in which the defibrillator 10 will be applied will vary widely. Defibrillation could take place in the victim""s home, on board an airliner or ship, on the street, or any other of a variety of locations. The geographic location of the defibrillation is an environmental characteristic that substantially affects the time required to get more advanced cardiac care on scene with the patient as well as the transport time needed to get the patient 14 to a hospital. It would be desirable that the behavior of the defibrillator 10 be optimized according to transport time.
In many situations such as a drowning, cardiac arrest is preceded by respiratory arrest. It has been found that cardio-pulmonary resuscitation (CPR) is best applied more aggressively before attempting defibrillation in such cases. It is thus desirable that the defibrillator behavior be modified for such applications to emphasize the use of CPR before attempting defibrillation. The application of CPR can be monitored by the defibrillator 10 with feedback given to the user 12. In U.S. application Ser. No. 08/965,347, titled xe2x80x9cExternal defibrillator with CPR prompts and ACLS prompts and Method of Usexe2x80x9d, filed Jun. 30, 1999 and assigned to the assignee of the present invention, the incorporation of prompts for CPR and other cardiac care is discussed.
The location of the defibrillator such with the staff of a public swimming pool or life guard facility would allow optimization of the defibrillator behavior for resuscitation of drowning victims. It would therefore be desirable that the behavior of the defibrillator 10 can be optimized for maximizing the resuscitation efficacy and patient safety based on the environment characteristics in which the defibrillator 10 is to be applied.
In accordance with the present invention, a medical device that is configurable for optimal behavior across a broad spectrum of patients, users, and circumstances is provided. The defibrillator is an example of a medical device having a user interface that typically includes front panel buttons, a liquid crystal display (LCD), and an audio speaker. The behavior of the defibrillator as reflected through the user interface is determined according to a set of set up parameters.
A set of environmental characteristics that represent the patient population, the user population, and the possible circumstances are first determined. The environmental characteristics are chosen that are relevant to determining the behavior of the defibrillator as reflected through the user interface.
The set of environment characteristics are then applied to a configure routine to determine an optimal behavior of the defibrillator. Optimal behavior of the defibrillation provides for achieving resuscitation of the patient in a manner which optimizes defibrillation efficacy and patient safety. Other optimal behaviors such as maximizing defibrillator battery life may also be achieved according to application requirements.
Maximizing defibrillation efficacy means that the defibrillation process is as reliable and error free as possible, given the particular patient, user, and circumstance. For example, an inexperienced user will require more frequent and detailed prompts from the defibrillator than a physician. A pediatric patient will typically require different defibrillation protocols such as lower energy levels than an adult patient for maximum defibrillation efficacy and patient safety. A patient suffering from respiratory arrest followed by cardiac arrest requires increased emphasis on CPR.
Maximizing patient safety means that the defibrillation process minimizes the possibility of injury to the patient and as well as to the user. For example, the inexperienced user may not know to refrain from touching the patient when the defibrillator is analyzing the heart rhythm. Such touching and movement introduce measurement artifacts which impede the process of detecting a shockable heart rhythm such as VF. The defibrillator can be adapted with increased user prompts to not touch the patient, adjusting the shock advisory algorithm to be more conservative in detecting shockable rhythms, and increased emphasis on artifact detection.
The optimal behavior can also be achieved using adaptation algorithms such as fuzzy logic and neural networks that allow the defibrillator to obtain measurements of the environmental characteristics and alter its behavior based on those measurements. Monitoring a pattern of usage may uncover differences in the environmental characteristics not anticipated when the defibrillator was originally configured. Providing for a control program that changes the configuration parameters allows the behavior of the defibrillator to be adjusted responsive to new environmental characteristics.
Defibrillators are one example of a medical device that may benefit from the ability to be configured to match the environmental characteristics. Other such medical devices may include cardiac monitors and drug delivery devices.
A feature of the present invention is to provide a method for configuring a medical device based on environmental characteristics.
Another feature of the present invention is to provide a configurable medical device.
A further feature of the present invention is to provide a configurable defibrillator.
Another feature of the present invention is to provide a defibrillator that may be configured according to environmental characteristics.
Another feature of the present invention is to provide a defibrillator capable of adapting to new environmental characteristics.
Other features, attainments, and advantages will become apparent to those skilled in the art upon a reading of the following description when taken in conjunction with the accompanying drawings.